Biology 1

Osmosis is the movement of water from an area of high water concentration (a dilute solution) to an area of low water concentration (concentrated solution) through a semi-permeable membrane. 

Active transport allows cells to take in substances against the concentration gradient and uses energy from respiration to do this. Cells are able to absorb ions from dilute solutions. 

When you exercise sugar, mineral ions and water are lost through respiration and sweat, causing you to become dehydrated therefore they need to be replaced. You may drink a sports drink which contains sugar, water and mineral ions, they are designed to balance the body's concentration of body fluids.  If the drink concentration matches the body fluids the solution is called isotonic.

Large organisms need exchange surfaces, effiecient exchange surfaces have:

- a large surface area so there is more places for diffusion to take place,

- thin walls creating a short diffusion path and

- a good blood supply.

The lungs contain the gaseous exchange surface which is increased by the alveoli. The alveoli have thin walls, a large surface area and a good blood supply. The lungs are also ventilated to maintain a steep diffusion gradient. 

When we breathe in:

- intercostal muscles contract

- the ribcage moves up and out, the diaphragm flattens

- the volume of the thorax increases

- the pressure in the thorax decreases and air is drawn in.

When we breathe out:

- the intercostal muscles relax

- the ribcage moves down and in, the diaphragm becomes domed

- the volume of the thorax decreases

- the pressure in the thorax increases and air is forced out

The iron lung - the person lay with their chest in a metal cylinder. When air was drawn out of the cylinder the persons chest moved up and they breathed in, when air was pumped in the chest moved down and they breathed out. The vacuum inside the cylinder formed a negative pressure. 

Bag ventilator - this is a type of positive pressure which forces air down the trachea. Positive pressure aids are smaller and easier to manage at home. 

The food we eat is digested in the gut into small, soluble molecules which are absorbed in the small intestine by the blood. The villi are an efficient exchange surface for the absorption of food molecules by diffusion or active transport. Villi increase the surface area for diffusion and are very thin. They also have a good blood supply close to the wall.

Oxygen and carbon dioxide diffuse in and out of leaves through the stomata. Leaves are flat, thin and have internal air spaces so diffusion can happen quickly and easily. Plants also lose water vapour through the stomata due to evaporation. 

Water and mineral ions are absorbed by the roots which have a large surface area. If plants lose water faster than its replaced by the roots, the stomata can close to prevent wilting. 

Water is taken up by the roots, it is then passed through the plant to the leaves. In the leaves the water evaporates and water vapour diffuses through the stomata. This movement of water through the plant is called the transpiration stream. 

Plants are adapted to reduce transpiration:

- waxy cuticles stops leaves from losing water through diffusion

- stomata on the underside of the leaves stops the sun reaching the leaf casuing the water to evaporate

- being able to close the stomata means no water can leave the plant

- having a small number of stomata means less places to lose water from